1. Field of the Invention
The present invention relates to a seatbelt retractor, and more particularly to a seatbelt retractor provided with a pretensioner for removing looseness in a seatbelt during a vehicle emergency, such as a vehicle collision.
2. Related Technology
Recently, seatbelt retractors have been provided with a pretensioner that causes a spindle to retract using a gas pressure generated by igniting an explosive or gas generating medium during a vehicle collision. Examples of such devices are shown in Japanese Patent Application Publication No. 2001-163182 (Patent Document 1), Japanese Patent Application Publication No. 2002-145012 (Patent Document 2), and Japanese Patent Application Publication No. 2002-154405 (Patent Document 3).
In a retractor 100 described in Patent Document 1, as shown in FIG. 6, balls 102 are moved through a pipe 103 by a gas pressure from a gas generator 101. The moving balls 102 engage with a ring gear 104 causing the ring gear 104 to rotate, and as a result, a spindle, that is integrally formed with the ring gear 104, is rotated in a retraction direction.
Further, the retractor 100 is applied to an apparatus, including an energy absorption mechanism that absorbs energy by causing a torsion bar to twist. The torsion bar twists such that a seat belt is unreeled when a load of at least a set value acts on the seat belt during a vehicle collision. A final guide portion 103a of the pipe 103 is formed so as to be easily deformable. Therefore, when the energy absorption mechanism is activated during an operation of the pretensioner such that the balls 102 are pushed in a direction heading back into the pipe 103, the final guide portion 103a of the pipe 103 flexes, thereby widening a passage of the balls 102. As a result, levers 104a of the ring gear 104 are prevented from catching on and stopping the balls 102.
Incidentally, with the retractor 100 described in Patent Document 1, the guide portion 103a, which is provided in a tip end portion of the pipe 103, is not fixed. Therefore, the balls 102 attempt to escape from the ring gear 104 due to an engagement angle between the ball 102 and the ring gear 104 during operation of the pretensioner. As a result, the amount of engagement between the ring gear 104 and the ball 102 decreases, leading to a reduction in an amount of transmitted force, and, therefore, the ring gear 104 cannot be rotated efficiently.